For receiving ultrasonic energy free of physical contact with a workpiece, as is desired for certain nondestructive test applications, optical arrangements are preferred. Several types of interferometers can be used, but particularly suited for this type of application is a transit time interferometer disclosed in U.S. Pat. No. 4,046,477, dated Sept. 6, 1977 of W. Kaule entitled "Interferometric Method and Apparatus For Sensing Surface Deformation of a Workpiece Subjected to Acoustic Energy". Other known optical receiving arrangments are shown in "Werkstoffprufung mit Ultraschall" (book), J. & H. Krautkramer, 3rd edition, Springer Verlag, Berlin/Heidelberg/New York (1975) pp. 162 et seq.